Difficulty in filtering relevant auditory information in background noise is one of the key features of autism spectrum disorders (ASD) and such filtering difficulties can significantly impair a person's social communication abilities. Parents and teachers often report that children with autism have particular difficulty attending to and understanding speech in noisy environments. These observations are supported by studies using standardized questionnaires to measure sensory functioning. While people with ASD have difficulties filtering speech information in background noise, there may be variability in filtering abilities, and some of this variability maybe be related to processing of: i) the auditory target (speech or non-speech signals), ii) auditory background noise (masker type), and iii) the ability of the auditory system to spatially separate the target from the masker (spatial release from masking). The physiological basis for the ability to filter relevant auditory information is believed to be due to regulation of cochlear activity by the CNS via descending auditory pathways-the olivocochlear efferent system. The medial olivocochlear (MOC) efferent system mediates active micromechanical contractile properties of cochlear outer hair cells (OHCs) which then modulate inner hair cell afferent firing rates. Moreover, the contractile activity of the OHCs can be evaluated in human subjects, because their contractions generate acoustic signals (otoacoustic emissions;OAEs), which can be recorded in the external ear canal, making it possible to directly measure auditory filtering processes at the cochlear periphery. It has previously been shown that adolescents and children with ASD have reduced MOC efferent feedback strengths using transient OAEs (TrOAEs). In Aim 1, we will investigate auditory filtering and spatial release from masking ability in adolescents with high functioning autism and typically developing controls, using both speech and musical tones as targets, and both speech-shaped and synthesized babble noise as maskers. We will use psychophysics and adaptive tracking to measure target thresholds in the different conditions to evaluate whether ASD is associated with impaired performance on speech-specific listening tasks. In Aim 2, we will measure cochlear MOC efferent feedback strength using two different otoacoustic emission-based tests: distortion-product OAEs (DPOAEs) and transient OAEs (TrOAEs) with binaural broadband stimulation to maximally activate MOC efferent feedback. We will test the hypothesis that MOC efferent feedback strength and R/L ear symmetry is impaired in ASD. Information gained from these studies will allow us to determine if a non-invasive measure of efferent feedback strength can serve as a physiological indicator of auditory filtering capabilities in this disorder. PUBLIC HEALTH RELEVANCE: This research will advance our understanding of how individuals with autism can hear speech sounds in the presence of background noise. This ability to filter relevant auditory information is critical for speech perception and the social use of language more generally. Using miniature speaker-microphone earplugs, we will also measure acoustic signals (otoacoustic emissions) generated by sensory cells in the inner ear as these emissions are suppressed in the presence of background noise. We will determine if individuals with autism have reduced noise-induced suppression of these emissions, and if such autism-specific differences in emissions are related to auditory filtering capabilities in this population.